The Xray Machine

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The X-ray Machine

• Applied Science

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The electromagnetic spectrum

• Remember back to GCSE. The EM Spectrum includes
  waves from Radio to Visible Light to Gamma
  Radiation.
• Waves like visible light cant travel through our
  bodies.
• X rays travel a lot faster so they can.

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So how do X rays produce images?

• We consist largely of water.
• This is easy for X rays to pass through.
• They can pass through us onto a metallic film.
• This will produce a shadow of our body.
• Different tissues in the body absorb X rays to
  different extents

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Air, Tissue and Bone..

• Because we are mostly water, our soft bits look
  the same as far as X rays are concerned.
• There are only 3 tissues that are differentiated
  Air, Soft tissue and Bone.
• Bones absorb X rays the most, so cast the
  brightest shadow.
• Air hardly casts a shadow so looks black.

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Example The lungs

• In this X ray of the lungs we can see that the
  air casts little or no shadow and looks black.
  The soft tissue looks grey and the bones have
  absorbed the X Rays the most and look white.

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Why do bones absorb X-rays?

• Bones contain Calcium.
• Calcium is a metal.
• Metals will absorb X-rays.
• This is why the photographic film used during
  examinations is metal!

Dental X-ray films
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Using X-rays on soft tissue

• X-rays are not limited to being used to view
  bones.
• Adding a contrast can extend the use of them to
  soft tissue too.
• Barium is a heavy metal and the liquid sulphate
  can be used as a meal or as an enema to show up
  soft tissues such as the oesophagus or colon.

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Barium Contrast

• Here is an X-ray of the colon following a Barium
  Enema.
• The Barium salt coats the lining of the colon and
  then air is pumped in to distend the bowel.
• The metal salt absorbs X-rays casting a bright
  shadow onto the film

The Barium is white, air is black. This method
can detect tumours.
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The X-ray machine

• The heart of an X-ray machine is an electrode
  pair -- a cathode and an anode -- that sits
  inside a glass vacuum tube. The cathode is a
  heated filament, like you might find in an older
  fluorescent lamp. The machine passes current
  through the filament, heating it up. The heat
  sputters electrons off of the filament surface.
  The positively-charged anode, a flat disc made of
  tungsten, draws the electrons across the tube

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• The voltage difference between the cathode and
  anode is very high, so the electrons fly through
  the tube with lots of force. When a speeding
  electron collides with a tungsten atom, it knocks
  loose an electron in one of the atom's lower
  orbitals. An electron in a higher orbital
  immediately falls to the lower energy level,
  releasing its extra energy in the form of a
  photon. It's a big drop, so the photon has a high
  energy level -- it is an X-ray photon.

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• The entire mechanism is surrounded by a thick
  lead shield. This keeps the X-rays from escaping
  in all directions. A small window in the shield
  lets some of the X-ray photons escape in a narrow
  beam. The beam passes through a series of filters
  on its way to the patient.

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• A film on the other side of the patient records
  the pattern of X-ray light that passes all the
  way through the patient's body. The X-ray film
  uses the same film technology as an ordinary
  camera, but X-ray light sets off the chemical
  reaction instead of visible light

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Are X-rays safe?

• X-rays are useful, but they can be harmful.
• When they were first used, doctors patients
  became over exposed and suffered radiation
  sickness.
• The problem is that X-rays are a form of ionising
  radiation.
• This can cause sickness or worse, cancer.

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Ionising Radiation

• When normal light hits an atom, it can't change
  the atom in any significant way.
• But when an X-ray hits an atom, it can knock
  electrons off the atom to create an ion, an
  electrically-charged atom.
• An ion's electrical charge can lead to unnatural
  chemical reactions inside cells. Among other
  things, the charge can break DNA chains.
• A cell with a broken strand of DNA will either
  die or the DNA will develop a mutation.
• If a lot of cells die, the body can develop
  various diseases.
• If the DNA mutates, a cell may become cancerous,
  and this cancer may spread.
• If the mutation is in a sperm or an egg cell, it
  may lead to birth defects

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Despite all that..

• X-rays are still safer than surgery.
• They are very useful in medicine and security.
• What precautions are taken for the patient and
  radiographers?